A dormer is a structural element of a building that protrudes from the plane of a sloping roof surface. Dormers are used, either in original construction or as later additions, to create usable space in the roof of a building by adding headroom and usually also by enabling addition of windows.
Often conflated with the term 'dormer', a dormer window is a window set into the dormer. Like skylights, dormer windows are a source of light and ventilation for top floors, but unlike skylights (which are flush with the roof surface) they also increase the amount of headroom in the room and allow for more usable space.
The main types of dormer are:
- Gable fronted dormer: the front of the dormer rises to a point at the ridge of the dormer roof. Also known as a dog-house dormer.
- Hipped roof dormer: the roof slopes back from front of structure to a point farther back.
- Flat roof dormer: the roof of the dormer is flat.
- Shed dormer: Often used in gable-roofed homes, a shed dormer has a single-planed roof, pitched at a shallower angle than the main roof.
In contrast to the above “roof dormers”, another type of dormer locates the window flush with the wall plane above, or more often through, the cornice line. This is the wall dormer.